1. Field of the Invention
This invention relates to lubricating oil and grease compositions, and more particularly to lubricating compositions having improved anti-wear/extreme pressure and/or anti-oxidant properties.
2. Description of the Prior Art
Anti-wear additives are chemicals which are added to lubricants to prevent destructive metal-to-metal contact in the lubrication of relatively moving surfaces. Plain mineral oils provide good lubrication and protection against excessive wear just as long as a film of oil is maintained between the relatively moving surfaces. This kind of lubrication, termed "hydrodynamic," is governed by the parameters of the lubricant, principally its viscosity. When the pressures or rubbing speeds between the moving surfaces increase to the point where the film of oil can be squeezed or wiped out, metal-to-metal contact begins to occur, often over a significant portion of the lubricated area. This kind of lubrication, termed "boundary lubrication," is governed largely by parameters of the contacting surfaces such as surface finish, metal shear strength and the coefficient of friction between the metals involved. Unless these parameters can be chosen to meet expected pressures and rubbing speeds, destructive metal-to-metal contact will occur. Such destructive contact manifests itself in various ways including scoring, scuffing, ridging, rippling and, in extreme cases, welding, leading to a catastrophic deformation and/or complete destruction of the lubricated components.
Anti-wear additives, which are added to many lubricants to prevent such destructive results from occurring, appear to function by reacting with relatively moving surfaces under boundary lubrication conditions to form an adherent solid lubricant film which has a lower shear strength than that of the metal surfaces. It is thought that this film takes over the task of lubrication when metal-to-metal contact occurs, thus protecting the metal surfaces from damage.
Over the years, the development of satisfactory oil and grease compositions for preventing excessive wear under high pressure, high temperature and/or high speed conditions has received much attention and numerous additives have been proposed for such service. Among these additives are compounds that generally contain lead, sulfur, phosphorus, halogen (principally chlorine), and carboxylate salts, organic phosphates and phosphites. The list also includes chlorinated waxes, sulfurized unsaturated organic compounds, heavy metal sulfides such as lead sulfide and molybdenum disulfide, and antimony thioantimonate. However, many of these materials are expensive and also extremely toxic. There is therefore a need for lubricating additives which are environmentally benign and inexpensive to use. The present invention provides such an additive.